This invention relates to novel compositions for treating skin tissues, particularly human skin tissues subject to drying, chapping, abrasion, and other forms of irritation. This invention specifically relates to sustained-release compositions for treating the skin tissues described above.
xcex1-hydroxy acids are commonly used in cosmetic formulations to treat skin tissue, frequently as an adjunct with other ingredients. The acids are used to remove dead and dying skin cells and produce a treated skin surface with a more healthy, youthful appearance. Some specific xcex1-hydroxy acid formulations have been used in shampoos, facial creams, and cuticle creams. xcex1-hydroxy acids, despite their beneficial properties, can nevertheless be irritating to body tissue if applied in too high a dosage or if applied to body tissue which is particularly sensitive to the acids.
Cyclodextrins are another class of compounds used in a variety of formulations to provide a sustained or controlled release of chemicals which can be complexed or chemically bound by the cyclodextrins. Cyclodextrins have been used in agricultural fertilizer and biocide formulations to control the release of biocides and fertilizers for the plants. Many chemical processes are also capable of being regulated and controlled through the use of cyclodextrin complexes which release chemical reactants in a graduated manner to control and sustain a desired property of the composition. Corrosion inhibitors and preservatives are examples of such compositions. Because of their complexing properties, cyclodextrins can be used to remove certain materials from other substances. Undesirable color and odors from processed foods, as well as undesirable ingredients such as caffeine from coffee, are examples. And because of their ability to release complexed materials gradually from the cyclodextrin molecule, cyclodextrins have been used in pharmaceutical compositions to enhance and control the bioavailability of active pharmaceutical compounds to the patient. Also, as with foods, cyclodextrins can be used to remove undesirable odors and tastes from pharmaceutical compositions.
Chemically, cyclodextrins are a group of cyclic oligosaccharides built up from a number of glucopyranose rings. The most common of the cyclodextrins are produced from six, seven, or eight glucopyranose rings and are referred to as xcex1-, xcex2-, and xcex3-cyclodextrins. Cyclodextrins have some degree of water solubility, and this is a property which ordinarily is advantageously used to produce their complexing ability with other molecules, referred to as guests. The term xe2x80x9cguestxe2x80x9d is used to refer to the compound which is trapped and complexed within the cyclodextrin molecule. In addition to the use of water as a solvent, other solvents can be used to permit cyclodextrins to form complexes with a number of other guests which may not be complexed using water with cyclodextrins.
Cyclodextrins perform their many complexing functions because of their molecular structure. Their molecular structure can be analogized to that of a doughnutxe2x80x94a cylindrical configuration with a cavity or hole in its center. The materials to be complexed are trapped within the hole or cavity of the cyclodextrin molecules and held there through a number of different binding mechanisms. The size of the hole or cavity, both its diameter and depth, is influenced by the number of glucopyranose rings in the cyclodextrin molecule, and the size of the cavity plays a critical role in the complexing of different chemical compounds. Although it is commonplace to have an approximately equimolar ratio of guest molecules to cyclodextrin molecules, it is equally possible to have, in the case of some low molecular weight molecules, more than one guest molecule complexed within the cyclodextrin molecular cavity. On the other hand, if the cavity is too large and the guest is too small, the guest may pass through the cavity and not be bound at all. With some high molecular weight guests, more than one cyclodextrin molecule can be required to form an adequate and complete complex with the guest. But if the guest molecule is too large for the cyclodextrin cavity, even several cyclodextrin molecules may not be able to bind the guest to temporarily inactivate its active moieties. This, in turn, produces an ineffective complexing of the guest and an ineffective controlled release of the formulation. This may be satisfactory if the partially complexed guest is to be removed because of its undesirability in the final formulation, but is quite unsatisfactory if the guest is complexed with the expectation that its activity will slowly be released upon use.
As a consequence of the cyclodextrin molecular cavity, the guest to be complexed, the reason for the complexing and the solubility of the guest in water or other solvents, it is not always possible to predict which guest molecules can be complexed by which cyclodextrin molecules to produce a particular desired effect. Considering the intended use of the cyclodextrin-guest composition and the environmental conditions under which the composition will be used, it becomes even more difficult to predict whether any chosen cyclodextrin formulation will perform adequately for its intended purpose.
The present invention relates to a cyclodextrin composition comprising a cyclodextrin and an xcex1-hydroxy acid wherein the xcex1-hydroxy acid is complexed by the cyclodextrin. The invention further relates to the use of the above composition to treat skin tissue, particularly skin tissue on, beneath and around the eyes, and the lips. The invention further relates to the above composition in combination with a ribbed applicator of the type shown in the accompanying drawings. The invention also relates to a topical pharmaceutical or cosmetic composition comprising the above composition and a pharmaceutically or cosmetically acceptable adjuvant for treating or applying to skin tissue. Finally, this invention relates to a method for treating skin tissue comprising the application of the above topical composition to skin tissue.
Without wishing to limit the invention to any particular theory of operation, it is believed that the xcex1-hydroxy acid or acids in the present compositions are gradually, over time on the skin, released from the cyclodextrin to benefit the skin. This xe2x80x9csustained releasexe2x80x9d feature allows the composition to be applied only once or twice daily (it can be applied more frequently if desired) and still get substantially continuous benefits. The present combination of xcex1-hydroxy acid/cyclodextrin can advantageously be included in cosmetic products, for example, lip make-up or eye make-up, so that such products provide an immediate cosmetic appearance enhancement while, at the same time, providing longer term benefits to the skin. The xcex1-hydroxy acids are believed to penetrate the skin, if at all, to only a very limited extent.